you may check if that actually available and there are tables in it by:
$ docker exec -it -u postgres tryton-postgres psql
postgres=# \c tryton
You are now connected to database "tryton" as user "postgres".
tryton=# \dt
//<here a plenty of tables>
tryton=# \q
Have you tried this?? What is the result?
—————
Also, it worth modifying in the container /etc/trytond.conf
adding the clause:
[web]
listen=0.0.0.0:8000
root=/var/lib/trytond/www
[database]
uri = postgresql://postgres:<db_password>@postgres:5432/
<db_password> is “mysecretpassword” in the example above…